Additive Options

The Economist has a write-up on 3D printing (that made slashdot). I found a lot of misunderstandings about the current state of the technology in the comments, and of course that is a call to arms. I'm not sure about a "revolution" as the Economist claims, but I do think the additive manufacturing (a.k.a direct digital manufacturing, rapid prototyping/manufacturing, 3D printing, additive layer manufacturing/fabrication, etc.) technologies will take up increasing space in our "toolbox" for making stuff. There are an exciting variety of systems available today for a variety of different materials.

Here's one very misinformed comment I'd like to address:

3-D printing works by laying and melting blocks of plastic to each other on the order of a mm. In no way at all, 0% in fact, is it tractable to any other type of manufacturing that exists with good reason. Material bonding is incredibly weak using this process and just not possible with certain types of material.
Metals can't be formed in this manner, and even if you re-engineered the machine to be able to inject and cool metals in small deposits, the structure would be absolute junk. It's purely a materials thing, unless we invent a material with magical properties, 3-D printing will make a marginal difference in manufacturing.
Joe_sd comment on Economist

And another from someone who claims to be an engineer who understands the manufacturing process:

Can we at present have an engine block, crank shaft of high speed rotor, impeller made by this 3D layering technology?
The answer is big No, for obvious reasons and inherent limitations.
I have serious doubts about the writer of this article being an engineer, having insight in to complexities of manufacturing processes.
Its more of a creative flight of fancy.
visiontunnel comment on the Economist

Good old Joe_sd is right about one particular method of 3D printing that all of us hobbyists are very familiar with. Fused Deposition Modeling (FDM) works by extruding layers of hot plastic that stick together (but the inter-layer strength is not like a fully consolidated part like you'd get from injection molding). There are research machines that do 3D welding of metals, which is very similar to FDM plastic (but you get consolidation between layers because the weld pool melts the previously deposited material). Of course, there are a great many other options for additive manufacturing beyond FDM, and those make metal parts for industry today.

EOS sells Direct Metal Laser Sintering (DMLS) machines that can "print" Titanium, Inconel, and Stainless Steel parts. 3DSystems also sells similar laser-based machines with a more limited range of alloys available. Arcam sells machines that use electron beams to print parts in Aluminum or Titanium. These process now result in fully dense metal parts with properties equivalent to (or in some cases "better than" because of tight process control on the input material) wrought parts.

If you want to print your own metal part in Titanium, one of Shapeways competitors i.materialise runs a Titanium printing machine. Be prepared for a little bit of sticker shock though, if you're used to ordering plastic parts off Shapeways or from our local friends at Fabbr.

Well that's neat that we can print metal parts, but what about 3-D printing only being able to make a "marginal difference in manufacturing"? According to this article GE is looking seriously at 3D printing aircraft parts since these parts can be more highly optimized than a CNC'd or cast part. A single kilogram weight savings is worth $100k over the life of an air-frame because of fuel savings. Maybe that's just "marginal", but if you're an airline, you live or die on razor thin margins: kilos and drag counts matter.

Here's another comment that I think is pretty uninformed:

3D "printing" (I would actually call it "molding"), while looks promising, will take years or even decades to start delivering anything meaningful other than miniature prototypes made of plastic compounds.
rajeev_sh comment on the Economist

What I love most AM that we'll see better, more innovative products get to market faster and with less waste.
This won't all happen over night, but you are living in the past if you think it won't happen.
trippytom comment on the Economist